It is known, e.g. from the following patents and other publications of record in the above-identified applications:
U.S. Pat. No. 3,921,550 PA1 U.S. Pat. No. 3,794,230 PA1 U.S. Pat. No. 4,013,026 PA1 U.S. Pat. No. 3,782,310 PA1 U.S. Pat. No. 3,973,507 PA1 U.S. Pat. No. 4,013,025 PA1 U.S. Pat. No. 3,162,154 PA1 U.S. Pat. No. 3,903,818 PA1 U.S. Pat. No. 3,713,408 PA1 U.S. Pat. No. 4,030,430 PA1 German utility model (Gebrauchmuster) No. 73 30 505 PA1 German utility model (Gebrauchmuster) No. 74 38 034 and PA1 German utility model (Gebrauchmuster) No. 73 19 362 to provide devices for the edge-parallel stitching of two or more fabric workpieces forming a stack, together along an edge seam with a sewing machine in which the fabric stack is advanced past the stitching location by fabric-feed dogs or presser feet constituting the usual fabric-feed means.
The sewing machine can be a conventional automatic sewing machine having an arm overhanging the stitching plate from which the fabric-feed dogs emerge or an arm from which a presser foot depends, to displace the workpieces in a predetermined sewing direction.
In the arm, the needle is reciprocated generally transversely to the stitching plate or table, usually in a more or less vertical or slightly inclined needle path. Such machines have been used for a variety of automatic sewing operations, for example, the stitching of seams in trouser legs, the sewing of pocket pieces into trousers, the stitching of the seams of shirts, blouses and jackets and, indeed, for a variety of applications in the garment-making field.
In general, an apparatus of the type described can include a fabric-feed sewing machine, in which the fabric-advancing or feed device is the feed dogs which are disposed in or below the work table or stitching plate, a workpiece-guide device located upstream of the stitching location in the direction of advance of the workpiece therepast and hence upstream of the feed dogs, and a drag clamp which is generally affixed to the stack of workpieces to be sewed together at a location remote from the starting of the seam so as to exert a force opposite that applied by the feed dogs, thereby stretching the workpieces and enabling them to pass in the proper orientation past the stitching location.
The workpiece-guide device can comprise a plurality of spaced-apart plates which lie parallel to the plane of the stitch plate and are interposed between the layers of fabric to be sewn together. In addition, the guide includes a guide surface or wall disposed laterally of the needle path and along which the edge of the fabric stack is intended to be guided.
The drag-clamping device engages the ends of the fabric stack remote from the portion thereof through which the needle passes during the inception of the stitching seam and can move with the fabric along a predetermined path while exerting a force in the opposite direction upon the workpieces. This, as already indicated, maintains the workpieces taut during the stitching operation.
Such devices are known, e.g. from the aforementioned copending applications and some of the other references mentioned above, and can be used with effectiveness for sewing, in edge-parallel relationship, a plurality of fabric layers which are to be joined together in an edge seam and which are comparatively long. Trouser legs, for example, are in this category.
With such devices, the ends of the fabric pieces remote from the stitching location are fixed in relation to one another by the drag clamping device so that, as the stack of fabric layers is drawn past the stitching location, the stitched seam can proceed without monitoring or control and without relative shifting of the fabric layers.
In conventional sewing installations of this type, the drag-clamp device is entrained with the fabric until just before the end of the fabric reaches the workpiece-guide device which, as previously indicated, is located at the upstream side of the needle path. At this point, the clamp of the drag unit opens and releases the end of the workpiece stack.
From this instant on, the sections of the fabric layers which are drawn past the needle location are no longer fixed relative to one another with the result that the stitching process over these sections is not always edge-parallel as is desired or required.